X-ray inspection systems, such as those used to characterize the contents of concealing enclosures such as baggage or cargo containers, typically employ an irradiating beam of specified cross-section that is swept relative to an object while portions of the beam that are either transmitted through the object or scattered by it are detected. Cross-sectional shapes of beams typically employed include fan beams, otherwise referred to as ‘fan-shaped’ beams, and pencil beams, where the characteristic dimension of the beam governs the spatial resolution of the system. The irradiating beam is characterized by an energy distribution of x-rays that is governed by the nature of the x-ray source and is invariant across the entire cross-section of the beam.
For a specified set of beam characteristics, the total photon flux through an object scales with the area of the beam. Thus, higher resolution, achieved by virtue of a tighter beam, is achieved at the expense of photon flux. Therefore, the thickness of the object through which radiation can be detected with a useful signal-to-noise ratio is also limited unless other parameters are changed. In the prior art, this trade-off is part of the design of the system that is performed prior to its operation in the field.